With the increasing competition in the semiconductor industry and the expense of producing integrated circuit devices, there is a need for quality assurance equipment to identify defective substrates as early in the fabrication process as possible. Surface profile equipment capable of resolving at a microscopic precision have been adapted for performing such quality assurance.
There are optical surface profilers available capable of measuring the surface profile of an opaque substrate. There also are spectrophotometric and ellipsometric devices available capable of measuring the thickness of a transparent layer on an opaque substrate at a single position on the sample. However, because the integrated circuit fabrication process includes adding layers of transparent film to light-absorbing or opaque substrates, there also is a need for an apparatus capable of measuring the surface profile of a transparent film on a light-absorbing or opaque substrate. Similarly, there is a need for an apparatus capable of measuring the subsurface profile of light-absorbing or opaque material through the transparent layer. Similarly there is a need to measure the film thickness profile of a transparent film on a light-absorbing or opaque substrate.